It is known that the heart rate of a healthy human varies over time within maximum and minimum heart rate limits. Absence of or diminution in heart rate variability has been found to be a useful indicator of fetal distress and apparatus has been developed to monitor fetal heart rate variability and alert medical personnel when variability is insufficient. Such a system constitutes the subject matter of application Ser. No. 571,380 filed on Apr. 24, 1975 in the name of George Hojaiban and assigned to the assignee of this invention. It has been found that the usefulness of the variability parameter is not limited to fetal monitoring and its measurement is at least equally beneficial in the case of neonatal monitoring.
Since a newborn is unable to communicate symptoms of illness, its bodily functions must be monitored by some external means in order for its condition to be determined. It is desirable to obtain a quantitative measurement of heart rate variability so that the degree of severity of condition of the neonate may be known. Furthermore, since the range of acceptable values of heart rate variability may differ from one neonate to another, depending upon size, weight, physiology, sex, and other characteristics, it is additionally desirable to have a capability for assigning tolerance limits for normal variability to each specific subject. Physicians may differ in their judgment as to what constitutes normal variability and when programming an alert system to sound an alarm for abnormal variability, it is desirable to permit the physician to preselect specific tolerance limits geared to the specific patient. Prior art variability monitors have only been able to determine whether variability is acceptable or unacceptable by qualitative measurement and to measure the period of time over which an acceptable or unacceptable condition exists in order to alert for variability.